For example, an ONO film formed by sequentially laminating SiO2, Si3N4, and SiO2 is used as an insulating film (dielectric film) for forming the capacitor of a dynamic RAM memory cell.
However, since the effective specific inductive capacity of the ONO film is as low as about 5, under the area restriction, a complicated shape is required to make the capacitor's dielectric film thinner and to expand the area when the film is used for a memory with a capacity of 256 Mb or larger. As a result, the process becomes very complicated.
On the other hand, the ferroelectric material with a perovskite crystal structure becomes noticeable as a material to be used in the future to form the insulating film of the capacitor for dynamic RAM because it has a very high specific inductive capacity ranging from a level of several hundred to several thousand.
The sol-gel method, CVD (chemical vapor deposition) method, sputtering method, etc., can be used to form the PZT film represented by Pb(Zr, Ti)O3 in the ferroelectric material. Among these methods, the sputtering method is the most appropriate one for mass production because it can uniformly form a film on an extensive flat portion without being affected by the roughness of the substrate.
However, when the PZT film is formed using the sputtering method, the density of the formed PZT crystallized nuclei on the substrate is low, and PbO evaporates in the formed film because of the low crystallinity. Consequently, it is relatively difficult to obtain a PZT capacitor with good electrical characteristics.
Platinum (Pt) is ordinarily used as the electrode substance for the PZT capacitor. However, since Pt is unable to reduce the silicon oxidized film, it cannot be directly adhered to the film. Therefore, after a Ti bonding layer with a thickness of about 50 nm is formed on the silicon oxidized film, Pt is deposited using the sputtering method or the electron beam heating deposition method.
When the PZT film is formed on said Pt using the sol-gel method, Ti diffuses through the Pt grain boundary to form TiO2 at the Pt-PZT boundary. Said TiO2 acts as the crystal nucleus when the PZT film is formed. In the sputtering method, however, since the evaporation of PbO is severe, it is difficult to form a PZT film better than that formed using the sol-gel method.
On the other hand, it is known that an electrode made of an oxidizing metal, such as iridium (Ir), or an electroconductive oxide, such as iridium oxide (IrO2), can be used to improve the polarization fatigue characteristics property of the PZT capacitor. However, when these substances are present on the substrate, the effect of forming nuclei by means of Ti diffusion cannot be realized even when a Ti layer is formed.
The purpose of this invention is to provide a method that can be used to form a high-quality ferroelectric film by forming good nuclei when using the sputtering method to manufacture a PZT capacitor or other ferroelectric capacitors using Ir or other electrode substances in addition to Pt for the electrode.